List of aliens in the game

These are the aliens in the game.

Sylvester (blue alien)
Balrog (Yellow alien)
Gus (Type-G) only can be killed using food
Destructor (Type-D) Missle shooter
Pychosquid (Type-P) Shoot him when red, stop when blue
Ulysses (Type-U) An advanced destructor that shoot penetrating missles.
Baliterus (Type-II) Two head alien
Cyrax (Final boss)